``The last two times when margin debt reversed and fell after a record-breaking spike, all hell broke loose. In 2000, it was simultaneous. In 2007, it was delayed by a few months. Today, on the surface, everything is still hunky-dory. The Dow is just fractions below its all-time high that it set on Wednesday. But beneath the surface, parts of the stock market are already coming unglued, and holders of momentum stocks have been eviscerated.''